The invention is directed to a wave digital filter (WDF) having delays and N-port adaptors, the N-port adaptors in turn having multipliers and adders.
Digital filters including digital equalizers digitally process samples of discrete values over time. Their fundamental function is described by their structure (signal graph) and their transfer function H(z) (ratio Y/X of the z-transform of output signal to input signal) The most important known structures of recursive digital filters or equalizers are direct forms of the higher order, cascade circuits of sub-structures of a lower order, parallel circuits of sub-structures of a lower order, wave digital filter ladder structures, wave digital filter lattice structures, and wave digital filter all-pass structures.
The following is a bibliography which is incorporated herein by reference with respect to wave digital filters, their theory and practice, their pseudo passivity, and the potential appearance of parasitic oscillations in such wave digital filters:
(1) Fettweis, A.: Digital Filter Structures Related to Classical Filter Networks, Arch. elektr. Ubertr. 25 (1971) 2, pp. 79-89.
(2) Fettweis, A.: Pseudopassivity, Sensitivity, and Stability of Wave Digital Filters, IEEE Trans. Circuit Theory 19 (1972) 6, pp 668-673.
(3) Fettweis, A.; Levin, H.; Sedlmeyer, A.: Wave Digital Lattice Filters, Int. J. Cir. Theor. App. 2 (1974) 2, pp. 203-211.
(4) Fettweis, A.; Meerkotter, K.: Suppression of Parasitic Oscillations in Wave Digital Filters, IEEE Trans. Circuits Syst. 22 (1975) 3, pp. 239-246.
(5) Fettweis, A.: Wave Digital Filters: Theory and Practice, Proc. IEEE 74 (1986) 2, pp. 270-327. Known problems in the implementation of recursive digital filters/equalizers are:
A. As a consequence of the hardware-conditioned, finite calculating precision, rough limit cycles and/or large-scale overflow oscillations can appear over the long duration, even given a zero signal at the input. This problem occurs in structures that are designed as direct forms of a higher order, or as cascades or parallel circuits of sub-structures of a lower order.
B. Not every fractional, rational transfer function that is arbitrarily allowable in view of order and values can be realized in a uniform way. This problem arises with increasing acuteness in the aforementioned wave digital filter structures.
C. The calculating requirements that limit the performance capability of the hardware increases greatly with increasing order of the transfer function given structures with direct forms of a higher order or with wave digital all-pass structures according to reference (5).
No known structure is thus without one of the above mentioned problems.
Previously, one has proceeded in the following way in order to resolve the existing problems.